1. Field of the Invention
This invention relates to a brake control device for vehicles which includes an anti-skid control function for preventing the wheels from skidding and a traction control function for preventing the wheels from slipping.
2. Description Of Prior Art
One of the examples of the brake control device of the above type is shown in a Japanese patent application published on Feb. 6, 1982 bearing publication number 57-22948 (the structure thereof is shown in FIG. 8 ). In the drawing, upon the braking operation by the depression of the brake pedal 1, the pressure in the master cylinder 2 is supplied to the wheel brakes via valves 3, 4 and 5. Under these situations, the pressure from the master cylinder is also supplied to the TRC inlet port 6 via passage L1 to change over the connection with the port 6a to the port 6c. Upon the anti-skid control operation, if the change over valve 3 is in an inoperative position as shown in FIG. 8, the pressure at the wheel brakes increase and if the valve 3 is in operative position, the pressure at the wheel brakes decrease due to the disconnection between the port 3a and the master cylinder and the connection between the port 3b and port 3c whereby the pressure at the wheel cylinders returns to the pump 7 via TRC inlet valve 6 and passage L4. Further, when the traction control is under operation, the pressure at the wheel brakes increase due to the connection between ports 3b and 3c.
Such conventional device, however, has a drawback that the structure of the TRC is very complex because of the too many components such as inlet valve 6, change over valves 3 and 4 or 5. It is therefore difficult to automatically add the components of TRC into the ABS system ( Anti-skid system ). Another drawback is that the TRC operation is not stable due to the high pressure passing through the three ports which may cause leakage of fluid and delay of response at the valves.